Radars are widely used for motor vehicles. Specifically, such a radar installed in a motor vehicle works to emit, from its antenna surface, radio waves over a given scanning area around the motor vehicle, and receive, by its antenna surface, radio waves reflected from an object lying in the scanning area based on the emitted radio waves. Based on the received radio waves, the radar works to measure a physical relationship between the object and the radar, such as a distance therebetween, a speed of the object when the object is moved, or the like.
Such a radar to be installed in a motor vehicle is preferably mounted on one end of the motor vehicle such that a radar transmissible cover, such as a bumper, is placed over the radar; this radar mounting arrangement is disclosed in, for example, Japanese Patent Application Publication No. 2003-240838.
The radar mounting arrangement set forth above causes power loss of emitted radio waves from the radar due to heat caused when the emitted radio waves are passed through the cover. The radar mounting arrangement also causes power loss of emitted radio waves from the radar due to influence between the emitted radio waves and reflected radio waves.
The power loss of emitted radio waves from the radar varies with change in the distance between the antenna surface and the cover. This is because the variations in the energy loss due to the distance between the antenna surface of the radar and the cover are believed to be caused by variations in a standing wave generated between the cover and the antenna surface of the radar. Such a standing wave is also believed to vary with change in the frequency of the emitted radio wave from the radar.
For this reason, it is important to reduce the influence of a standing wave generated between the cover and the antenna surface of the radar on the emitted radio waves from the radar to thereby reduce the power loss of the emitted radio waves therefrom.
Moreover, when radars are differently placed in motor vehicles, there are variations in the object measuring performances of the radars. In order to reduce the variations, it is proposed that each of the radars is commonly placed on an inner surface of the cover, such as the bumper, of each motor vehicle.
However, the arrangement of the radar on the inner surface of the cover may cause vibration of the cover and/or a slight impact thereto, resulting in damaging the radar.